I have to say, I bought into all of the diet myths before Mom was hospitalized. When I taught community college early education health classes (geared toward day care teachers) I even taught some of them. I still regret teaching my students that water intoxication was virtually impossible except among marathon athletes, the mentally ill, and people trying to dilute their urine in order to pass urine drug tests by drinking gallons of water.
Some of the water myths are harmless, but some are very dangerous. If you're drinking 8 - 10 glasses of tap or bottled water instead of other beverages, you're not doing yourself any harm, but if you are drinking it on top of other beverages, it is possible to be drinking too much water and not even know it. The myth that you should drink 1/2 oz per lb of body weight is probably harmless if you're of average weight, but could be dangerous if you're extremely overweight.
I do get on my soap box about this, because my mother nearly died, and now has permanently lost 40 - 50% of her kidney function because she bought into these myths. I'm biased, and I admit this, so I don't ask anyone to take my word for it, but to do your own homework.
I like this article, because it sums up, and disputes the most common water myths, but don't take one article's word for it either, do your own digging.
http://www.snopes.com/medical/myths/8glasses.asp